A variety of antigens may be detected in the serum of patients with hepatocellular carcinoma (HCC). The incidence and distribution of five antigens in 37 HCC and their relation to each other in a given tumor was examined by the peroxidase-antiperoxidase technique using formalin-fixed paraffin-embedded tissues. alpha 1-Antitrypsin was frequently expressed in HCC (73 per cent of cases), whereas alpha-fetoprotein and carcinoembryonic antigen were less common. HBsAg, but not HBcAg, was observed in tumor cells in seven of nine HCC from HBsAg-positive patients. In 20 HCC (54 per cent), two or more antigens, most frequently alpha 1-antitrypsin and alpha-fetoprotein, were detected. Double staining for simultaneous localization of two antigens in the same tissue section revealed that different antigens were usually present in different tumor cells, although some cells displayed two antigens simultaneously. These findings suggest that hepatocellular carcinoma cells are functionally heterogeneous, even if they appear histologically monomorphic.